In the field of civil engineering and construction (construction industry), a very important point for the maintenance of a concrete structure (e.g., a tunnel, a bridge, or a building) is to understand the position of corroded reinforcing bars in the concrete structure or the degree of corrosion of the reinforcing bars. However, currently, no convenient technique is available for nondestructively determining or evaluating the corrosion state of reinforcing bars in the interior of a concrete structure, and such determination or evaluation requires a long period of time and high cost.
There have been known apparatuses, including an apparatus for inspecting the state of, for example, reinforcing bars or steel frames in the interior of a concrete structure, which are magnetized by any cause (see Patent Documents 1 and 2); and an apparatus for measuring the amount of metal present (see Patent Document 3). However, these apparatuses do not actively utilize magnetization.
Thus, various methods have been employed for nondestructive inspection of a reinforced concrete structure, but most of the methods are intended to inspect deterioration of the concrete structure, or cavities, cracks, etc. which occur therein. Therefore, demand has arisen for a method for more conveniently inspecting corrosion of reinforcing bars in the interior of a concrete structure (i.e., in a special environment).
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2002-77953
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2003-185636
Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. H07-151731